1. Field of the Invention
The invention relates generally to multi-cylinder compressors for use in air conditioning systems for vehicles. More particularly, the invention relates to multi-cylinder compressors having a plurality of suction ports formed through a valve plate, in which the suction ports are spaced from each other so as to reduce noise or vibration, or both, generated by the compressor.
2. Description of Related Art
Referring to FIG. 1, a known, swash plate-type, multi-cylinder compressor 1 for use in an air conditioning system of a vehicle (not shown), is depicted. Compressor 1 includes a front housing 17, a cylinder block 16, a rear housing 18, and a drive shaft 10. Front housing 17, cylinder block 16, and rear housing 18 is fixably attached to each other by a plurality of bolts 15. Drive shaft 10 passes through the center of front housing 17 and the center of cylinder block 16. Drive shaft 10 also is rotatably supported by front housing 17 and by cylinder block 16 via a pair of bearings 11 and 12 mounted in front housing 17 and cylinder block 16, respectively. A plurality of cylinder bores 16a is formed within cylinder block 16, and cylinder bores 16a also are positioned equiangularly around an axis of rotation 20 of drive shaft 10. Moreover, a piston 25 is slidably disposed within each cylinder bore 16a, such that pistons 25 reciprocate on axes parallel to axis 20 of drive shaft 10.
Compressor 1 also includes a rotor 21, a crank chamber 30, and a swash plate 13. Specifically, rotor 21 is fixed to drive shaft 10, such that drive shaft 10 and rotor 21 rotate together. Crank chamber 30 is formed between front housing 17 and cylinder block 16, and swash plate 13 is positioned inside crank chamber 30. Swash plate 13 is slidably connected to each piston 25 via a pair of shoes 14 positioned between swash plate 13 and each of pistons 25. Swash plate 13 includes a penetration hole 13c formed therethrough at a center portion of swash plate 13, and drive shaft 10 extends through penetration hole 13c. Rotor 21 includes a pair of rotor arms 21a, and a pair of oblong holes 21b formed through rotor arms 21a, respectively. Swash plate 13 further includes a pair of swash plate arms 13a, and a pair of pins 13b extend from swash plate arms 13a, respectively. A hinge mechanism 19 includes rotor arms 21a, swash plate arms 13a, oblong holes 21b, and pins 13b, and rotor 21 is connected to swash plate 13 by hinge mechanism 19. Specifically, one of pins 13b is inserted into and slidably engages an inner wall of one of oblong holes 21b, and another of pins 13b is inserted into and slidably engages an inner wall of another of oblong holes 21b. Moreover, because each of pins 13b is slidably disposed within their corresponding oblong hole 21b, the tilt angle of swash plate 13 may be varied with respect to drive shaft 10, such that the fluid displacement of compressor 1 also may be varied.
Compressor 1 further includes a valve plate 40 having a vertical center axis 110 which is perpendicular to axis 20 of drive shaft 10, a discharge chamber 70, a suction chamber 80, and a suction gas inlet passage 60. Suction chamber 80 extends around discharge chamber 70. Moreover, valve plate 40 has a plurality of cylinder suction ports 90 and a plurality of discharge ports 101 formed therethrough. Specifically, referring to FIG. 2, each of suction ports 90 has a center portion 95, and center portions 95 are equiangularly spaced along an arc having a radius (R), i.e., angles θa′–θg′ formed between adjacent suction ports 90 are equal to 360°/N, in which N is the number of suction ports 90 formed through valve plate 40. For example, referring again to FIG. 1, when compressor 1 is a three-cylinder compressor, an angle of 120° (360°/3) is formed between adjacent suction ports 90, and when compressor 1 is a five-cylinder compressor, an angle of 72° (360°/5) is formed between adjacent suction ports 90. Similarly, when compressor 1 is a seven-cylinder compressor, an angle of about 51.4° (360°/7) is formed between adjacent suction ports 90.
Compressor 1 also may include an electromagnetic clutch (not shown). When the electromagnetic clutch is activated, a driving force from an external driving source (not shown) is transmitted to drive shaft 10, such that drive shaft 10, rotor 21, and swash plate 13 rotate about axis 20 of drive shaft 10. Moreover, swash plate 13 also moves back and forth in a wobbling motion, such that only movement in a direction parallel to axis 20 of drive shaft 10 is transferred from swash plate 13 to pistons 25. Consequently, each piston 25 reciprocates within its corresponding cylinder bore 16a. In operation, a fluid, e.g., a refrigerant, is introduced into suction chamber 80 via suction gas inlet passage 60. During a suction stroke of piston 25, the fluid flows through the corresponding suction port 90 into a corresponding compression chamber 50 which is formed by a top portion of a corresponding piston 25, the walls of a corresponding cylinder bore 16a, and valve plate 40. The fluid subsequently is compressed by piston 25 during a compression stroke, and the compressed fluid flows into discharge chamber 70 via discharge ports 101.
Nevertheless, during the operation of compressor 1, dynamic pressure pulsations in suction chamber 80 are generated by the reciprocating motion of pistons 25, and the dynamic pressure pulsations pass to compression chamber 50 during the suction stroke of pistons 25. Such dynamic pressure pulsations reduce a performance of compressor 1, and also increase noise or vibration, or both, within compressor 1. The dynamic pressure pulsations also may affect a timing of an opening or a closing, or both, of a suction valve (not numbered). In attempting to decrease this noise, vibration, or both, a method of designing such known, multi-cylinder compressors includes the steps of kinematically determining a mass flow rate within suction chamber 80, i.e., a mass of a fluid delivered to suction chamber 80 per unit of time. Moreover, based on known relationships for determining dynamic pressure pulsations in suction chamber 80, the method also includes the steps of increasing a depth 120 of suction chamber 80, and increasing a width 130 of suction chamber 80, in which a cross-sectional area of suction chamber 80 equals depth 120·width 130. Further, based on the known relationships, the method includes the step of increasing a mean radius of suction chamber 80, in which suction chamber 80 has a varying radius measured from a center of discharge chamber 70. Specifically, depth 120, width 130, and the mean radius of suction chamber 80 are inverse factors of the known relationship. Consequently, when the kinematic mass flow rate is factored into the relationship, increasing any of depth 120, width 130, and the mean radius of suction chamber 80 theoretically decreases the dynamic pressure pulsations within suction chamber 80.